Process for removing oxidizable fumes from heated air used to treat textile fibers

ABSTRACT

In a process for heat treating textile filamentary structures having a textile finish containing oxidizable components wherein a portion of said components are undesirably vaporized, the improvement for removing at least a portion of said vaporized components comprising directing said components through a gaspermeable structure having an oxidation catalyst for said textile finish in a finely dispersed form on the structure to oxidize said components to a more desirable state at about the same temperature range used to treat the textile structure. Specific oxidation catalysts disclosed are palladium and platinum. The process can operate at extremely high space velocities making the process feasible from an economic viewpoint.

United States atet 91 F ernandes et al.

[451 Apr. 3, 1973 [75] Inventors: l-larold Fernandes; William Henry Walsh, both of Newark, Del.

[73] Assignee: E. l. du Pont de Nemours and Company, Wilmington, Del.

[22] Filed: Sept. 9, 1970 [21] Appl. No.: 70,653

Related US Application Data [63] Continuation-impart of Ser. No. 812,506, Sept. 18, 1968, abandoned, which is a continuation-in-part of Ser. No. 706,816, Feb. 20, 1968, abandoned.

[52] US. Cl. ..423/245, 34/32, 34/72, 34/114 [51] Int. Cl. ..B01d 53/34 [58] Field of Search ..23/25, 4; 34/23, 26, 32, 36,

6/1956 Houdry et al ..34/36 X 7/1967 Keith et al. ..23/2 X Primary Examiner-Earl C. Thomas Attorney-Howard P. West, Jr.

[5 7] ABSTRACT In a process for heat treating textile filamentary structures having a textile finish containing oxidizable components wherein a portion of said components are undesirably vaporized, the improvement for removing at least a portion of said vaporized components comprising directing said components through a gas-permeable structure having an oxidation catalyst for said textile finish in a finely dispersed form on the structure to oxidize said components to a more desirable state at about the same temperature range used to treat the textile structure. Specific oxidation catalysts disclosed are palladium and platinum. The process can, operate at extremely high space velocities making the process feasible from an economic viewpointv 3 Claims, 2 Drawing Figures PATENTEDAPR3 I973 5,53

FIG-1 FIG- Z 80 INVENTORS mow FERNANDES WILLIAM HENRY WALSH BY a/ut ATTORNEY PROCESS FOR REMOVING OXIDIZABLE FUMES FROM HEATED AIR USED TO TREAT TEXTILE FIBERS CROSS REFERENCE TO RELATED" APPLICATIONS This application is a continuation-in-part of our copending application Ser. No. 812,506, filed Sept. 18, 1968 now abandoned, which is in turn a continuationin-part of our application Ser. No. 706,816, filed Feb. 20, 1968, and now abandoned.

BACKGROUND OF THE INVENTION This invention is concerned generally with the removal of oxidizable fumes from heated gases. More particularly, it is concerned with the process for the removal of oxidizable fumes from heated gases used for the treatment of temperature responsive yarns carrying an oxidizable finish containing organic components.

In many textile processing operations, it is necessary to apply a finish to the fiber, particularly synthetic fibers, in order to improve the running characteristics during the processing in subsequent applications. Frequently, in the processing of synthetic fibers, it is necessary to subject the fibers to a heat treatment in order to obtain or improve upon the desirable properties of the fiber. Such heat treatments tend to volatize the finish, which may be an organic material dispersed in water or may be a combination of volatile oils and waxes, which escapes as a fume commonly referred to as smoking. Such fumes escaping into the atmosphere not only may be irritating to the workers in the area but frequently condense on operating machinery causing problems in cleanliness, housekeeping, potential flammable conditions and even degradation of the quality of the textile product being produced. Many attempts have been made to eliminate the potential problems by the choice of formulation of the finish to avoid smoking components. However, it is not always possible to arrive at a suitable compromise between adequate finish requirements and reduction of smoking components. Other attempts to minimize the problems have included: extraordinary measures to make process equipment air tight to prevent escape of fumes; more sophisticated ventilation systems with increased capacity to exhaust fumes which may then require scrubbing and taller stacks or other conventional means for minimizing the potential for air pollution. Frequently, increased ventilation reduces the heating efficiency of the heat treatment process thereby requiring excess amounts of energy in order to provide the required degree of heat treatment.

While catalytic oxidation of fumes and organic vapors has been known in other fields, it has been necessary to operate such systems at high temperatures in order for the catalytic action to be effective. Such temperatures are generally about 300 C. or higher which are entirely unsuitable for synthetic textile heat treatments which generally require temperatures below about 250 C. The use of high temperature catalytic systems known in the prior art would require extensive cooling systems and an additional cooling step in a yarn heat treating process which is sensitive to temperature change and in which it is difficult to maintain the exact temperature conditions for proper heat treatment of the textile fibers.

SUMMARY OF THE INVENTION This invention provides a process for removing oxidizable fumes from a textile fiber heat treating medi- Another provision of this invention is to provide a process for the heat treatment of textile fibers carrying a finish. A further object is to provide a continuous heat treatment process for the synthetic textile fiber in the presence of volatile oxidizable finish in a manner that prevents the accumulation of finish on the fiber treatment apparatus.

With these and other objects in view, the process for controlling the concentration of oxidizable volatile textile finishes in heated air which has been used for textile processing comprises contacting the air and vaporized finish components with a catalyst at the process operating temperature within the range of about to 250 C. The particular choice of catalyst is, of course, dependent upon the temperature of the operating conditions and upon the nature of the oxidizable material.

The invention is an improvement in a process for heat treating textile filamentary structures having a coating of a textile finish containing oxidizable organic components with a hot gas at a temperature within the range of about 100 C. to about 250 C. whereby a portion of the organic components of said finish is undesirably vaporized and transported by said hot gas; wherein the improvement comprises removing at least a portion of said vaporized organic components from said hot gaswhich comprises directing said vaporized organic components through a gas-permeable structure having an oxidation catalyst for said textile finish in a finely dispersed form on the structure to oxidize said components to a more desirable state.

More particularly, from a mechanistic viewpoint, one embodiment of the invention is defined as in a process for heat treating textile filamentary structures having a coating of a textile finish containing oxidizable organic components with a hot gas at a temperature within the range of about l00 C. to about 250 C. whereby a portion of the organic components of said finish is undesirably vaporized and transported by said hot gas; the improvement of substantially removing said vaporized organic components from said hot gas which comprises adsorbing said components on an adsorbing porous solid having a surface area in excess of 50 mlg, driving off said components by continuously directing said hot gas through said adsorbent solid and contacting said components with an oxidation catalyst impregnated in and situated on said adsorbent solid to convert said components to carbon dioxide and water; said adsorbent solid being made by preparing a homogeneous aqueous mixture of a gel forming material and a decomposable catalytic salt, forming said mixture into a rigid structure by allowing the mixture to set and calcining said rigid structure to decompose said catalytic salt to its catalytically active state and to develop a network of pores in said structure. It is to be understood that applicant does not intend to be bound by any theory but that the above stated mechanism is what applicant believes to be an explanation of the process mechanics.

Other embodiments include gas-permeable structures of activated alumina granules and a ceramic honeycomb network housing the alumina dispersed thereon.

It is to be understood that textile filamentary structures refer to a tow, yarn or fabric of said filaments or to any other form to which the filaments may be while being heat treated.

Quite surprisingly, use of the adsorbent catalytic composition allows very high space velocities (about times that of the prior art) thereby making the practice of the present invention an economic reality.

While no specific apparatus is required for the utilization of the invention, it has been found suitable to insert a screened container containing the catalyst on a suitable carrier into the recirculation line of the heating medium.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic illustration of the yarn treating system of the invention.

FIG. 2 is a diagrammatic side elevation partially in section of a temperature control system for heat treating yarn incorporating an oxidation catalyst.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS Referring now to FIG. 1, it is seen that a thread line 10 passes through a heating chamber 2. Hot gas heated by heat exchanger 3 is circulated by a blower 4.

The hot gas volatilizes a portion of the finish on thread line 1 and is exhausted through duct 5 connected to the chamber 6 containing suitable catalytic material and thence to the intake of blower 4 for recirculation. The catalytic material can be held in a wirescreen basket. A wire mesh canister in the shape of a truncated annular cone has been found to be quite efficient.

FIG. 2 shows in diagrammatic form the embodiment of the invention used in practicing the examples which follow. Two rotatably driven rolls 12, 14 are positioned inside housing 32. Openings 34, 36 are provided for entry and exit of yarn 10. A blower 40, a heat exchanger unit 62 and a series of passages are arranged to form a substantially closed circuit which directs hot air from the heat exchanger 62 into the interior of the roll elements 12 and 14 through inner concentric tubular elements 47, thence along the exterior of the roll elements and back to the inlet of blower 40. A wirescreen basket 70 containing catalytic material is posi tioned in the inlet line 72 to blower 40.

An access door 52 pivotally mounted at hinge 61 is provided for housing 32. When access door 52 is opened, damper 50 which is linked to and actuated by door movement through link 56 moves toward its closed position and acts to prevent cold air from being pulled in by blower 40. In addition, when door 42 is opened, air inlet 54 is opened by movement of the upper portion of door 52 above hinge 61.

To prevent any outside cool air currents from entering through openings 34 or 36 or any other opening that may exist, the housing 32 is kept under a slight positive pressure. This is done by having a small air inlet opening 48 near the suction of blower 40.

Coil 62 is a condensing vapor heating means, wherein the temperature at which vapor in the coil condenses is held constant by holding coil pressure at a constant level. A variation in the heating demands on coil 62 (represented by a raise or fall of the input temperature of the air to be heated) merely affects the amount of vapor which condenses in the coil which varies the amount of heat (of condensation) given out by the heating means.

By the continuous catalytic oxidation of the finish fumes near the source of the fumes and at the temperature of operation of the heat treatment process the accumulation and decomposition of the volatilize finish is prevented.- Without using the catalytic treatment of this invention, finish accumulates in the gaseous medium and the apparatus necessitating frequent cleaning of the apparatus to remove the coating of finish on the ap paratus parts. Without such cleaning sufficient finish may collect and drip on the textile product being produced. Such drips cause nonuniform spots on the product which often lead to streaks and other dyeing defects in articles produced from the textile product. Buildup of finish also leads to partial decomposition of the finish which forms a tacky coating on the apparatus and unsatisfactory operation of the apparatus.

In operation, the flow rate of the air is maintained at such a high level and the area of the coil 62 is such a large size that the desired temperature'of heat transfer is maintained very accurately within small limits despite the exothermic reaction of the catalyst in basket 70.

Using continuous catalytic operation with apparatus similar to that shown in FIG. 2 and processing a 50 denier nylon yarn coated with an oxidizable textile finish solution comprising diester and bisphenol as described by Tolliver in US. Pat. No. 3,387,996 typical temperatures recorded at points A, B, C, D were as follows:

TEMPERATURE C.

A B c D 198.0 192.0 l87 212 1911.0 195.0 187 212 198.0 194.0 187 212 198.0 193.5 187 212 As seen from these readings, the temperature across the catalyst bed actually decreases a small amount (A- B). The lower temperature at the discharge side of the catalyst than at the entrance can be attributable to losses in the system at this point exceeding the temperature rise due to the oxidation of the finish oil fumes.

The invention will be further illustrated by the following examples, which, however are not intended to be limitative.

EXAMPLE I A catalyst adsorbent composition useful in practicing the present invention is prepared as follows:

l. A solution is prepared by dissolving the following materials; 716 parts of a 50 percent manganese nitrate solution, parts nickel nitrate hexahydrate, 145 parts cobalt nitrate hexahydrate and 300 parts chromium trioxide (CrO,) in sufficient distilled water, at a temperature of 30 C. to produce 3,000 parts of solution.

2. There is separately prepared 500 parts of ammonium carbonate dissolved in five thousand parts of distilled water.

3. With the solution produced in item I being rapidly agitated, the ammonium carbonate solution produced in item 2 also at 30 C. is added to the solution of item 1 until the pH has reached 6.4 plus or minus 0.2.

4. The slurry is digested for one hour at 30 C. plus or minus 3 C.

5. The slurry is filtered and washed with 4,000 parts of distilled water. The filter cake thus derived is that called for in the preparation of the catalyst adsorbent in ensuing instructions.

6. Six hundred parts of the filter cake derived in item 5 is charged to a 4 liter ball mill containing 2% liters of grinding balls having 16 X 16. cylindrical shape.

7. Charged also the ball mill are 100 parts of JU-activated carbon, a powdered activated carbon derived from coconut shells and having a surface area of 1,200 square meters per gram, an absorptivity in excess of 60 minutes as determined by ASTM standard test and as ash content of less than 2 percent sold by Bamabey- Chaney Company of Columbus, Ohio. Charged also to the ball mill is 100 parts of C-333 alumina hydrate which has been calcined previously at 400 C. for 3 hours. The C-333 alumina is that sold under this designation by the Aluminum Company of America and is a power passing 100 percent through a 325 mesh screen and having an ultimate particle size of approximately 0.5 micron. It has a chemical composition of aluminum hydroxide, Al(OI-l) with apparent density 0.2 to 0.3 gram per cubic centimeter as determined by the Scott volumetric method. Next, the ball mill is charged with 2,400 parts ofLudox SM. Ludox SM" is a tradename designation of the assignee for colloidal silica which is an aqueous collidal sol containing approximately 15% S characterized by extremely small particle size averaging about 7 millimicrons.

8. The ball mill is rotated for 16 hours and then the milled slurry is removed and dried at 150 C. for 16 hours.

9. It is then calcined at 350 C. for 30 minutes.

10. The catalyst is then crushed and screened to the proper mesh size which is 6 to 10 mesh.

11. One thousand parts of the granules produced in item 10 is moistened with 1,000 parts of a palladium nitrate solution containing 1.5 parts elemental palladi- 12. The moist granules are dried and calcined for 30 minutes at 250 C.

13. The granules are then moistened a second time with 1,000 parts of a solution of chloro platinic acid containing 0.5 part of elemental platinum.

14. The granules are then dried and calcined at 250 C. for 30 minutes.

The catalyst adsorbent composition as prepared above is placed in a wire-screen basket. The basket is placed in the recirculation line of the yarn heat treating system as illustrated in FIG. 2 and further described in Bagnoli et al., US. Pat. No. 3,161,484, dated Dec. 15, 1964. The screen basket completely covers the crosssection of the recirculation line. The geometry of the recirculation line, screened container and volume of the catalyst composition is such that the space velocity of the circulating heated air is within the range of about 475,000 to 635,000 cubic feet of gas at standard conditions per hour per cubic foot of the catalyst composition. The screened container is placed upstream of the blower in order to oxidize the fumes before they contact any working surfaces and are therefore located as close as possible to the source of the fumes.

The heat treating apparatus is operated at a temperature of 190 C. to draw a continuous filament polyamide yarn coated with an oxidizable textile finish solution consisting of 98 percent of the di(2-ethylhexanoate) of a mixture of polyethylene glycols having an average molecular weight of 238 and 2 percent of 4,4- thio-bis-(3-methyl-6-tert-butylphenol) as described in Tolliver, US. Pat. No. 3,387,996. The concentration of oil fumes in the hot air medium is measured by extracting the oil from a volume of the air medium using carbon tetrachloride solvent, evaporating the solvent and weighing the residual oil. The concentration is expressed as milligrams of oil per standard cubic meter of air. The sample of air is taken downstream of the catalyst at the discharge port of the blower. Within 1 hour of operation, the finish oil in air concentration is measured at milligrams per standard cubic meter and there is visually observed a marked decrease in oil smoke intensity. The measured oil concentration continues to decrease over a period of days as residual oil films previously condensed on the equipment surfaces vaporize. After 1 month, the measured concentration is below 50 milligrams per standard cubic meter, the I equipment surfaces are dry and free of oil and oil smoke cannot be visually detected. This performance is sustained continuously for more than 9 months.

In comparison, the same process conditions are used to heat treat yarn of the same description except that no catalytic treatment is provided for the heated air medium. The finish oil concentration is measured at 700 milligrams per standard cubic meter after a few hours and after several days reaches over 1,000 milligrams per standard cubic meter.

EXAMPLE 11 A heat treatment system similar to that described in Example I is used to process a continuous polyamide filament except that the operating temperature is only C. When no catalytic treatment is provided in the heated air medium, the accumulation of condensed oil and decomposition products on interior surfaces of the heat treatment system is evident within 24 hours and the accumulation of tarry and oily buildup is so profuse at the end of 6 weeks that it interferes with efficient operation of the heat treatment system unless the system is shut down and cleaned.

A wire-screen basket is filled with a modification of the catalyst and carrier described in Example I and the basket is inserted so as to completely traverse the crosssection of the recirculation line'as described in Example l. The catalyst is prepared in the same manner as in Example I except that twice as much of the uncalcined filter cake is used 1,200 parts) in step 6.

Although the same process conditions are used, no condensation of oily deposits is evident and interior surfaces of the heat treatment system remain dry and clean after 6 weeks of operation, enabling continued operation without shutdown for cleaning.

EXAMPLE III A heat treatment system identical to that described in Example 11 and using the same finish oil is operated at only 130 C. During normal operation without a catalyst treatment, accumulation of decomposition products on interior surfaces of the heat treatment system is observable after several days of operation.

Although the accumulation on the interior surfaces is not as severe as that described in Example II at the end of 6 weeks, the accumulation at 130 C. is obvious. When the heat treatment system is treated with the catalyst as described in Example II, no accumulation is observable at the end of 6 weeks at 130 C.

EXAMPLE IV A catalytic composition is prepared using the procedure of Example I with the following changes: In step 6, only 300 parts of the filter cake is used. In step 7, 160 parts of activated carbon and 140 parts of calcined alumina hydrate is used. In step 1 1, only 0.5 part of elemental palladium is used and step 13 (platinum) is omitted.

The catalyst thus prepared is placed in the heat treating system as in Example I and the oil content of the air measured. After 1 hour, the concentration is about 150 milligrams per standard cubic meter and there is visually observed a marked decrease in oil smoke intensity. After 1 month, the measured concentration is about 300 mg. per standard cubic meter and the concentration continues to rise at the rate of about 40 mg. per standard cubic meter per month.

Though this catalyst formulation does not perform as well as the formulation of Example I, it is a vast improvement over no catalyst as without the catalytic treatment the oil concentration within a matter of hours climbs to greater than 1,000 mg. per standard cubic meter.

EXAMPLE V A wire-screen basket identical to that of Example I, except that the catalyst used in the basket is 0.15 percent by weight of reduced platinum deposited on '16 inch diameter activated alimina spheres of high surface area, is placed in the recirculation line of a heat treatment system identical 'to that described in Example I. These spheres are sold by Oxy-Catalyst Inc. and are designated as A-l25 pellets.

Oil concentrations are measured in the range of 50 milligrams per cubic meter, as contrasted to levels of 700 to 1,000 milligrams in a system without the catalyst treatment.

The equipment surfaces are dry and free of oil and oil smoke cannot be visually detected.

This performance is sustained continuously for 6 weeks and there is no indication the performance will not continue longer.

EXAMPLE VI A catalyst of 0.15 percent by weight reduced platinum deposited on a ceramic honeycomb structure coated with a high surface area alumina is used in place of the wire-screen basket in Example V. A suitable ceramic honeycomb is 3/16 inch cell size, cross flow Torvex which is a cellular structure of 96 percent alumina (Al,0,) or mullite (3 Al,0,/2 Si(),), having high peripheral surface area per unit volume, low resistance to flow, high refractoriness, thermal stability, wide range chemical inertness and black body thermal radiation characteristics sold by the E. I. du Pont de Nemours & CompanIy.

Results comparab e to Example V are achieved during five weeks of continuous operation and there is no indication the performance will not continue longer.

EXAMPLE VII A heat treatment system similar to that described in Example I is used to process a continuous polyamide filament except that the operating temperature is only 180 C. When no catalytic treatment is provided in the heated air medium, the accumulation of condensed oil and decomposition products on interior surfaces of the heat treatment system is evident within 24 hours and the accumulation of tarry and oily buildup is profuse at the end of 1 week.

A wire-screen basket is filled with the catalyst described in Example V and the basket is inserted so as to completely traverse the cross section of the recirculation line as described in Example I.

Although the same process conditions are used, no condensation of oily deposits is evident and interior surfaces of the heat treatment system remain dry and clean after 1 week.

While the catalytic operation has been illustrated for oxidizing fumes being recirculated in a yarn treating system, the low temperature operation is also useful for oxidizing fumes that are being exhausted from a heat treating system. For example, the catalytic material could be placed in duct attached to exhaust blower 82 (FIG. 2).

It is apparent that many changes and modifications of the disclosed process may be made without departing from the scope of the present invention which is, accordingly, intended to be limited only by the scope of the appended claims.

What is claimed is:

1. In a process'for heat treating textile filamentary structures having a coating of a textile finish containing oxidizable organic components with a continuously recirculating hot gas containing oxygen at a temperature maintained within the range of about C. to about 250 C. whereby a portion of the organic components of said finish is undesirably vaporized and transported by said hot gas; the improvement of removing at least a portion of said vaporized organic components from said hot gas which comprises directing said gas carrying said vaporized organic components through a gas-permeable structure at a space velocity within the range of about 300,000 to about 1,000,000 ft. /hr., said structure having a surface area in excess of 50 square meters per gram and having an oxidation catalyst selected from the group consisting of palladium and platinum and mixtures thereof in a finely dispersed form on the structure to oxidize said components to a more desirable state at a temperature within said range.

2. The process as in claim 1, wherein the gas-permeable structure is comprised of activated alumina granules.

3. The process as in claim 1 is comprised ofa ceramic honeycomb coated with activated alumina. 

2. The process as in claim 1, wherein the gas-permeable structure is comprised of activated alumina granules.
 3. The process as in claim 1 is comprised of a ceramic honeycomb coated with activated alumina. 